The investigators have been asked to write a chapter for a textbook tentatively titled The Obstetric Management of Multifetal Pregnancy. Dr. Powers has recently written a thesis for his Masters Degree. The subject of the thesis was prophylactic interventions in twin pregnancy, and as part of the literature review, data from NCHS on the rate of increased survival of twins with increasing gestational age were reviewed. Dr. Kiely has reported on birth weight specific mortality of twins as ascertained from the New York City fetal death, live birth and infant death files. Dr. Fowler has compared survival rates of black and white twins and singletons from the 1960 and 1983 U.S. Linked Birth/Infant Death Data Sets from NCHS. The authors have been asked to consolidate these reports and expand them into a chapter for the above mentioned text.